The computer, information, and entertainment industries produce and consume annually hundreds of millions of disk-shaped substrates, principally silicon wafers, and aluminum, plastic, glass, or other multi-component disks. In the fabrication of computer CPU chips, silicon wafers are processed through multiple fabrication steps which include repeated application and selective removal by CMP and scrubbing of variously conductive, non-conductive and semi-conductive materials before the resulting micro-circuits are complete and separated into individual dies.
Aluminum, glass, and other composite disk substrates are typically over-coated with magnetic, optical, or magneto-optical materials in the fabrication of HDDs, CDs, DVDs, and other data storage products.
Substrates must be buffed, polished, etched, cleaned, and otherwise prepared repeatedly during the fabrication process. This is true for both wafer and disk substrates. In the semiconductor manufacturing industry, integrated circuit devices designed with complex, and extremely fine and precise multi-layered structures, require highly clean and prepared surfaces.
In the field of magnetic and optical media disks, ever-increasing areal density translates into exacting requirements for disk cleaning and preparation. Defects resulting from improper, income-plete, or insufficient substrate buffing, polishing, cleaning, or other preparation produces decreased yield and increased time and cost.
By way of example, a microscopic contaminant of size on the order of 0.1 micron left on the surface of a hard drive disk substrate could cause the hard drive to fail, as the clearance between the drive head and the substrate magnetic media is only on the order of 0.0125 microns (0.5 micro-inches). Accordingly, the standard of cleanliness of hard drive substrates currently required in the Hard Drive industry is no more than 1 particle per side of size no greater than 0.1 micron. A greater number of contaminants, both in size or in number, will result in rejection of the substrate disk and a reduction in yield. This is extremely significant to this industry, as the cost to the consumer per megabyte of hard drive capacity, on the order of $40 per MB in 1985, is now on the order of <0.125 cents per MB, or <$1.25 per Gigabyte. With incredibly thin profit margins, it becomes essential that substrate cleaning systems, e.g., scrubber apparatus and methods, are fast, highly efficient and result in high yield of substrates that meet particulate cleanliness standards.
To meet the ever-increasing demands for cleaner substrates, both semiconductor and disk industries have adopted rotating brush scrubbing as the standard cleaning procedure. Each brush station includes one or more pair of brushes. The brush material is usually polyvinyl alcohol (PVA), but other materials such as mohair and nylon can be used. These systems are either single-substrate, one-at-a-time operations, or continuous streams, one-after-the-other.
A particularly leading-edge, continuous, brush cleaning system comprises a linear cascade of paired, counter-rotating brushes maintained on parallel spaced mandrels, in the nip of which are propelled the wafers or disks to be cleaned. These “Cascade Scrubber” systems are shown in U.S. Pat. Nos. 6,588,043 (wafer scrubbing) and 6,625,835 (hard drive disk substrate scrubbing), the subject matter of which are hereby incorporated by reference as if reproduced here to the extent required for completeness of disclosure of cascade scrubbing apparatus.
However, very small particles (less than 1 micrometer in size), lodge in the extremely fine crevices and trenches of the substrates. While cascade brush scrubbers alone can remove particles down to on the order of 0.1 micron, ongoing developments in the field of increasing hard drive areal density requires removal of even smaller particles. Ultra-fine particle dislodgement from the crevices and trenches is currently done in batches in ultrasonic and megasonic baths, either before the cascade scrubbing stage, after that stage, or both before and after (preferred), as the sonic energy can dislodge debris particles in the crevices. Once the particles are dislodged from substrate crevices by the sonic energy in the ultrasonic/megasonic baths they can be removed from the surface of the substrate by brush scrubbing.
Thus, in the present industry practice, there is alternating batch, continuous, batch cleaning operations that require special collection and handling devices and robot transfer system as the process operations switch from batch to continuous and back again. For example, in the Hard Disk substrate cleaning process, initial cleaning may be ultrasonic bath (batch), followed by cascade brush scrub (continuous), followed by megasonic bath (batch), followed by DI dip-and-pull drying (batch). At each change of process type, batch to continuous, there are special handling problems to resolve. As through-put rate requirements increase to meet output demands and to maintain cost margins, these process interface problems become more complex and costly to resolve.
Accordingly, there is a need in the art for a cleaning system that can keep up with the increasingly stringent requirements for substrate cleanliness, and can keep up with increased through-put demands by eliminating one or more interface problems. The invention meets this need in the art by providing apparatus and methods for simultaneous use of cascade brush scrubbing and sonic energy to clean wafer and disk surfaces.